End dump fifth wheel trailers have an elongated, open-topped body for holding bulk materials and a hydraulic cylinder for lifting the front end of the body into a tilted configuration so that the bulk material dumps from an openable rear end gate. End dump trailers typically have supporting axles and wheels disposed near the rear end of the body and a kingpin disposed near the front end of the body for attachment to the fifth wheel of a conventional tractor (i.e., semi-truck). End dump trailers may be further classified as either frame-type trailers or frameless-type trailers depending on how the body is supported.
Frame-type end dump trailers have a main frame extending continuously between the kingpin and the supporting axles and wheels disposed near the rear of the trailer. Both the kingpin and the supporting axles are connected to the main frame rather than to the body. During transport over the road (“hauling”) the body bears on the main frame, whereby the weight of the body and its cargo is supported by the main frame. The body is pivotally attached to the rear of the main frame for tilting during dumping. The hydraulic cylinder is attached to the front of the main frame and lifts the front end of the body relative to the main frame, i.e., the main frame remains generally horizontal as the body is tilted for dumping. A disadvantage of frame-type end dump trailers is relatively high empty weight. The relatively high empty weight results from the need for the main frame to have sufficient strength to support the entire weight of the body and the cargo during hauling coupled with the need for the body to have sufficient strength to support the weight of the cargo as well its own weight when raised (i.e., tilted) by the hydraulic cylinder for dumping. Because total vehicle weight (including cargo) is often regulated by law, a higher empty trailer weight results in reduced net cargo capacity. A need therefore exists, for frame-type end dump trailers having lower empty weight.
Frameless-type trailers do not have a continuous main frame, but instead have a subframe mounted directly to a rear portion of the body. The supporting axles and wheels are connected to the subframe. The kingpin is disposed on a separate kingpin plate along with the hydraulic cylinder that lifts the front of the body to dump cargo. The kingpin plate is typically connected to the body by a pair of draft arms having front ends pivotally attached to the kingpin plate and rear ends pivotally attached to the body midway between the front and rear ends. The draft arms transmit force from the kingpin to body for pulling and braking the trailer, however, the draft arms to not provide any vertical support for the body. During hauling, the front end of the body is supported by the kingpin plate and the rear end of the body is supported by the subframe with its axles and wheels. Since there is no main frame extending between the kingpin plate and the subframe, the body must be strong enough to support its own weight and the weight of the cargo during both hauling and dumping. During dumping, the hydraulic cylinder on the kingpin plate lifts the front of the body (the kingpin plate itself remaining attached to the fifth wheel of the tractor) and the rear of the body pivots on the rear wheels while the draft arms maintain a pivoting connection between the body and the kingpin plate. An advantage of frameless-type end dump trailers is relatively low empty weight. The relatively low empty weight results from elimination of the main frame by providing a body with sufficient strength to support the entire weight of the body and the cargo during both hauling and dumping. The lower empty trailer weight results in increased net cargo capacity. However, the body of a frameless-type trailer needs higher strength since it is not supported by a main frame during hauling. A need therefore exists, for frameless-type end dump trailers having both higher strength and lower empty weight.
Aluminum alloys may be used in fabricating bodies for either frame-type or frameless-type end dump trailers to provide lower empty weight and higher net cargo capacity. Aluminum alloys are alloys in which aluminum is the predominant metal. The typical alloying elements are copper, magnesium, manganese, silicon, tin and zinc. Aluminum alloy compositions are registered with The Aluminum Association, a trade association based in Arlington, Va. Many organizations publish specific standards for the manufacture of aluminum alloy, including the Society of Automotive Engineers (“SAE”), ASTM International (“ASTM”), the American National Standards Institute (“ANSI”), the Deutsches Institut für Normung e.V. (“DIN”; in English, the “German Institute for Standardization”) and the International Organization for Standardization (“ISO”). The International Alloy Designation System is the most widely accepted naming scheme for wrought aluminum alloys. Each alloy is given a four-digit number, where the first digit indicates the major alloying elements, the second (if different from 0) indicates a variation of the alloy, and the third and fourth digits identify the specific alloy in the series. For example, the 6000 series of aluminum alloys comprise aluminum alloyed with magnesium and silicon. Well-known member of the 6000 series include alloys 6061, 6005 and 6005A.
Many aluminum alloys may be heat treated (i.e., “tempered”) to produce substantially higher yield strengths than the base alloy. A temper designation consisting of a dash, a letter and potentially one-to-three digit number is used following the alloy series number to designate the type and degree of tempering. For example, full soft (annealed) alloy is designated “−O” and alloy heat treated to produce stable tempers is designated using the “−T” series from “−T1” through “−T10” where the trailing number indicates the specific heat treatment process used. In some cases, annealed alloy is referred to as “−T0” rather than “−O”. Thus, for example: “6061-0 aluminum” (alternatively “6061-T0”) designates annealed 6061 alloy having a maximum tensile strength of about 18,000 psi and a maximum yield strength of about 8,000 psi; “6061-T4 aluminum” designates 6061 alloy that has been solution heat treated and naturally aged to have a maximum tensile strength of about 30,000 psi and a maximum yield strength of about 16,000 psi; and “6061-T6 aluminum” designates 6061 alloy that has been solution heat treated and artificially aged to have a maximum tensile strength of about 45,000 psi and a maximum yield strength of about 39,000 psi. Since the weight of the aluminum alloy does not change significantly between O/T0, T4 and T6 tempers, it will be appreciated that alloys having higher tempers such as T6 have a much higher strength to weight ratio than the base alloy (annealed). Thus, the use of high temper aluminum alloys such as 6061-T6, 6005-T6 and 6005A-T6 for fabricating trailer bodies can provide much higher strength for hauling and dumping at substantially lower weight than use of the untempered (annealed) base alloys.
Although many aluminum alloys including, for example, the 6000-series alloys such as 6061, 6005 and 6005A, are highly weldable using, e.g., tungsten inert gas welding (TIG) or metal inert gas welding (MIG), the use of high temper alloys such as T4 and T6 in large welded structures may be problematic. After welding, the properties of high tempered alloys in the vicinity of the weld are typically degraded to those of −O/T0 (annealed) alloy, a loss of strength of around 80% compared to the original T6 tempered alloy. Although it is possible to re-heat-treat the material by controlled reheating to restore the high temper, this is typically impractical where the structure is a large fabrication such as a trailer body. Thus, after welding T6 tempered alloy, industry guidelines recommend the design strength of the alloy material adjacent to the weld to be taken as the strength of the annealed base alloy (−O/T0) instead of the tempered alloy. Even relatively routine workshop procedures involving the heating of tempered aluminum alloy are not advised, because the material may be damaged (e.g., reduced temper and reduced strength) with no visual sign. A need therefore exists, for aluminum bodies for end dump trailers fabricated from tempered aluminum where the loss of temper due to welding the tempered aluminum is avoided.
Due to the rough use encountered while loading, hauling and dumping bulk materials from an end dump trailer, damage to the body may occur. If the body is made from tempered aluminum alloy, repairing a damaged section with welding will result in loss of temper and the associated loss of strength in the aluminum alloy material. A need therefore exists, for aluminum bodies made of high temper aluminum alloy that can be repaired without welding